None listed
Conditions
Brief summary
Exercise associated hyponatraemia is a life threatening condition that can occur in (ultra-) endurance athletes who exercise for long periods of time. The primary risk factor is overhydration with hypotonic fluid, i.e. drinking at a greater rate than any excess can be excreted (Hew-Butler et al 2015). However, other factors can play a role, including sodium losses (Godek, et al 2008) and intakes (Vrijens & Rehrer, 1999). Although ingesting a beverage with 18 mmol/L sodium reduces the rate of decline in plasma sodium when compared with water (during endurance exercise in the heat) it still does decline. Sweat sodium ranges from ~30-80 mmol/L and studies with 60 mmol/L sodium (oral rehydration solutions) in clinical situations (at rest), in which plasma sodium is compromised via losses, result in improved hydration and normalisation of plasma sodium. Therefore, we intend to test the efficacy of a beverage with 60 mmol/L sodium, when consumed in slight excess (i.e. approximately matching body mass loss) throughout longlasting exercise in the heat (34 degrees C) in healthy, endurance trained individuals. The purpose of this study is to establish whether increasing the concentration of sodium in a beverage (~ 3 times that normally in sports drinks), can keep blood sodium concentration from decreasing during longlasting exercise in the heat, when fluid is ingested in amounts to nearly match body weight loss. The hypothesis is that ingesting a beverage with 60 mmol/L of sodium during 3 h of cycling in the heat will prevent the fall in blood sodium that typically occurs with a beverage with 18-20 mmol/L of sodium. We will utilise a randomised cross-over intervention in which participants will perform exercise in the heat, and will ingest a beverage with one of two concentrations of sodium (20, 60 mmol/L) and then repeat the trial with the alternate concentration.
Interventions
We will utilise a randomised cross-over intervention in which participants will perform two, 3 h exercise trials (cycle ergometry @ workload to elicit 55% VO2max, determined in a graded maximal exercise test on a separate day) in the heat (34 degrees C, controlled climate chamber), periodically ingesting a beverage, with either 60 or 20 mmol Na+/L and the rate of plasma sodium change monitored. The experimental protocol is based upon earlier work (Vrijens & Rehrer, 1999). The beverages will u
We will utilise a randomised cross-over intervention in which participants will perform two, 3 h exercise trials (cycle ergometry @ workload to elicit 55% VO2max, determined in a graded maximal exercise test on a separate day) in the heat (34 degrees C, controlled climate chamber), periodically ingesting a beverage, with either 60 or 20 mmol Na+/L and the rate of plasma sodium change monitored. The experimental protocol is based upon earlier work (Vrijens & Rehrer, 1999). The beverages will use a base of Gatorade (5.94% glucose 20 mmol Na+/L ) to which NaCl will be added to bring to 60 mmol Na+/L for intervention beverage. (a pre-trial will be done for acceptability and if unpalatable or gastrointestinal distress a mix of NaCl and sodium citrate will be used). The volume given will be determined by net body mass losses in a 1 h exercise pre-trial conducted on a separate day prior to experimental trials under the same conditions (specified amount of water given). The amount of fluid provided in 3 h experimental trials will be at a rate (given every 15 min) to replace mass loss observed in the 1 h trial (i.e. slight excess since some mass loss is due to substrate metabolism). This will be measured out in advance, chilled and provided to participants who will be told to ingest completely as quickly as possible. No other beverage will be ingested. A researcher will be continually supervising participants during exercise trials. During trials heart rate and rectal temperature will be continually monitored. If age predicted heart rate maximum or a core temperature of 39.5 degrees C is reached exercise will be stopped. Experimental trials will be separated by at least 7 days. The evening before trial 1 litre of sports drink (Gatorade [5.94% glucose 20 mmol Na+/L] provided) will be ingested. Breakfast is to be consumed 2 h before the first experimental trial, which will be of their choice, but they will be required to eat this same meal before the second trial. They will also be instructed to drink 1 L of a sports drink (provided) the evening before each trial. On the day of the trial before coming to the laboratory, they may drink water ad libitum, but may ingest no other foods or fluids after breakfast. In addition, the subjects will be instructed to refrain from strenuous exercise 24 h before each trial.
Sponsors
School of Physical Education Sport & Exercise Sciences, University of Otago
Study design
Allocation
Randomised controlled trial
Intervention model
Crossover
Primary purpose
Prevention
Masking
Blinded (masking used) (Subject, Outcomes Assessor)
Eligibility
Sex/Gender
Male
Age
18 Years to 55 Years
Healthy volunteers
Yes
Inclusion criteria
Endurance trained males. This does not need to be cycle specific.
Exclusion criteria
Smokers On prescription medications (except nutritional supplements) or other drug use (except caffeine), Have kidney disease or diabetes, Contraindications to participate in maximal exercise.
Outcome results
None listed